The Mode of Action of Urease. 



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97 (914) 



The mode of action of urease. II. 



By Donald D. Van Slyke, Gotthard Zacharias and 

 Glenn E. Cullen. 



[From the Hospital of the Rockefeller Institute for Medical Research, 



New York.] 



The action of the generated ammonium carbonate in retarding 

 the action of urease is due to the alkalinity of the carbonate. 

 When the solution is kept neutral by a proper phosphate mixture 

 the products have no effect on the velocity of the reaction. Elimi- 

 nation of the effect of the products makes urease a particularly 

 favorable enzyme with which to study the reaction between enzyme 

 and substrate. The results indicate that the action consists of 

 two successive reactions: combination of enzyme and substrate in 

 definite proportions; and decomposition of the compound, the 

 urea being thrown off as ammonium carbonate; each of the two 

 reactions consuming a definite portion of the total time. Formula- 

 tion of these relations leads to the equation / = - log \--z, 



M c a — x d 



t representing the time required for the decomposition of x amount 

 of the initial substrate amount, a; c is a constant representing the 

 velocity of combination of enzyme and substrate, d representing 

 the velocity of decomposition of the complex. The values of c 

 and d can be determined independently, and one can thereby 

 determine whether changes in conditions affect the combination 

 reaction, or that of decomposition. Neutral salts retard the 

 combination. Alkaline reaction hastens it, but retards the de- 

 composition. Slightly acid reaction greatly retards the combina- 

 tion, affecting the other reaction but little. The independent 

 variation of the two phases of the process of enzyme action 

 explains some previously obscure facts in regard to the effect of 

 alkalies, acids, and other substances on enzyme action. 



